GABA CONTROL OF LHRH RELEASE IS DEPENDENT ON THE STEROID MILIEU

The effect of GABA in controlling luteinizing hormone releasing hormon e (LHRH) release from isolated hypothalamic fragments containing the m ediobasal hypothalamus, suprachiasmatic nucleus, and the preoptic area (MBH-SCN-POA) was tested under different hormonal conditions with an in vitro superfusion method. GABA significantly decreased LHRH release under conditions of low, chronic levels of estradiol (E2) treatment b ut had no effect on tissue obtained from animals in proestrus. This su ggests that the inhibitory effect of GABA is only manifested during ce rtain stages of the estrous cycle characterized by negative feedback a nd low E2.